3 Watt FM transmitter

Posted on Jul 6, 2012

Connect two 24 V / 3 W bulbs in parallel to the output and set the right frequency on PLL. Now turn on the transmitter. You should tune it on a receiver. Maybe you might stretch coils of the L1. Fix the L1 in position when the tuning voltage (on C4) is in range 4-9 V. Then use C15, C16 and C17 to adjust the highest power (the highest light of the bulbs). Then you can connect antenna and audio signal. Adjust R1 until the audio sounds as loud as the other stations. With good antenna (dipole placed outdoor and high) the transmitter has very good coverage range about 1500 meters, the maximal coverage range is up to 20 km. Power supply: 12 V stab., 0,7 A. RF power: 3 W. Impedance: 50-75 ohm. Frequency range: 88-107 MHz. Modulation: wideband FM.

3 Watt FM transmitter
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Parts list: Capacitors: C1 - 4,7 uF (electrolytic) C2 - 0,22 uF (electrolytic) C3, C4, C12 - 100 pF (ceramic) C6, C9, C11, C13, C14, C19 - 1 nF (ceramic) C7, C8 - 10 pF (ceramic) C10 - 8.2 pF (ceramic) C18 - 22 pF (ceramic) C15 - trimmer 47 pF C16, C17 - trimmer 60 pF C20, C5 - 100 nF (ceramic) C21 - 470 uF (electrolytic) Coils: (All coils are free-standing air-core types, wound of 0,7 mm Cu wire, 6 mm internal diameter.) L1, L6 - 4,5 coils L3 - 2,5 coils L4 - 1,5 coils L2 - 6,5 coils around R9 resistor L5 - 9,5 coils L7 - 3,5 coils Resistors: R1 - 10 k pot. R2 - 4,7 k R3, R4, R5, R8, R10 - 27 k R6, R16 - 10 k R7, R15 - 470 R9 - 100 R11 - 270 R12 - 1 k R13 - 43 R14 - 10 Diodes: D1, D2 - BB109G, BB409 or BBY31 Transistors: T1 - BC547C (BC548C, BC547B) T2 - BFR91A (BFR96) T3 - BFR96S T4 - 2SC1971

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